The present invention relates generally to a system and method for improving the ignition characteristics of certain internal combustion engines, and particularly to a system and method for reducing pocket sparking at the spark plug (or plugs) used in an engine, such as a direct fuel injected two-stroke engine.
Internal combustion engines generally have one or more cylinders through which one or more pistons move in a reciprocating manner. Each piston is connected to a crankshaft by a connecting rod which delivers force from the piston to the crankshaft to rotate the crankshaft. Power to drive the piston is provided by igniting a fuel-air mixture disposed in the cylinder on a side of the piston opposite the connecting rod. The fuel-air mixture is ignited by some type of ignition device, such as a spark plug.
A conventional spark plug includes a base to which a mounting shell is attached. Typically, the mounting shell includes external threads that are threadably engaged with a corresponding spark plug opening in the engine. The spark plug typically includes an insulative core that extends through the base and into the interior of the mounting shell. A nose of the insulative core extends into the mounting shell and tapers inwardly, creating an annular space or pocket between the core nose and the interior surface of the mounting shell.
A central electrode extends axially through the insulative core such that it has an exposed tip on the mounting shell side of the insulative core. On an opposite side of the insulative core, the electrode has a connecting end designed for connection to the engine""s ignition system. The ignition system provides sufficient electrical energy to create a spark at the electrode tip.
Typically, the spark is created between the electrode tip and a second electrode that is electrically connected to the mounting shell, and thereby grounded to the motor. Upon sufficient input from the ignition system, electricity arcs between the electrode tip and the secondary electrode, thereby creating the spark that ignites the fuel-air mixture within the cylinder.
In certain engine applications, the central electrode tip and the core nose become coated with deposits, such as carbon deposits. This can result in the electrical charge traveling along the deposits and jumping to the mounting shell at the base of the pocket formed between the insulative core nose and the mounting shell. When this xe2x80x9cpocket sparkxe2x80x9d ignites the fuel-air mixture in the pocket, a late combustion or a slow traveling flame front results and leads to late combustion of the fuel-air mixture in the combustion chamber. The late combustion reduces the power of the engine and often results in a detrimental effect, known as xe2x80x9cknockingxe2x80x9d. This problem is particularly pronounced in fuel injected engines in which the spark plug electrodes are located directly within the fuel spray injected into a given cylinder.
It would be advantageous to provide a system and methodology for preventing ignition of the fuel-air mixture at the base of the core nose due to pocket sparking.
The present invention features a fuel injected, two-stroke engine system designed to prevent undesirable ignition characteristics. The system includes a two-stroke engine having an internal combustion chamber defined by a wall. A fuel injector is mounted to the engine and extends through the wall into communication with the internal combustion chamber. The injector is designed to discharge a fuel spray into the internal combustion chamber. A spark plug also is placed in communication with the internal combustion chamber. The spark plug includes a base and a shell extending from the base. The shell defines a hollow interior and is coupled to a first electrode, such as a J-type electrode. A second electrode extends through at least a portion of the hollow interior and is surrounded by an insulating layer. A closure member extends from the shell into proximity with the insulating layer to substantially enclose the pocket formed between the interior surface of the shell and the exterior surface of the insulating layer.
According to another aspect of the present invention, a spark plug has been designed to reduce pocket sparking. The spark plug includes a base and an insulative core disposed through the base. The insulative core includes a core nose extending axially outwardly from the base. An electrode is disposed within the insulative core and includes a tip exposed at a distal end of the core nose. Additionally, a shell is connected to the base and includes a terminal end that encircles the core nose. The terminal end is less distant from the base of the spark plug than the distal end of the core nose. In other words, the core nose extends beyond the shell. Furthermore, a second electrode is coupled to the shell such that a spark can be created across the gap between the first and the second electrodes. Additionally, a lip extends inwardly from the terminal end towards the core nose to substantially enclose the pocket formed between the core nose and the shell, thus preventing pocket sparking.
According to another aspect of the present invention, a method is provided for reducing undesirable ignition characteristics in a fuel injected engine. The method includes injecting a fuel into a cylinder of an engine and igniting the fuel with a spark plug. The spark plug is of the type having an electrode surrounded by a mounting shell that forms a pocket between the electrode and mounting shell. The method further includes isolating the pocket to prevent detrimental pocket spark induced ignition during operation of the engine.